PICkit™ 3 Starter Kit User’s Guide
DS41628B-page 86 2012 Microchip Technology Inc.
3.13.5 New Registers
3.13.5.1 ENHANCED MID-RANGE
Flash program memory is also writable during normal operation. This is commonly
referred to as “Self-modifying code” or “Self-write”. This is achievable by implementing
a modified Harvard architecture.
3.13.5.1.1 EEADRx/EEDATx
When accessing the program memory block, the EEDATH:EEDATL register pair forms
a 2-byte word that holds the 14-bit data for read/write, and the EEADRL and EEADRH
registers form a 2-byte word that holds the 15-bit address of the program memory loca-
tion being accessed.
3.13.5.1.2 EECON1
Control bit EEPGD determines if the access will be a program or data memory access.
When clear, any subsequent operations will operate on the EEPROM memory. When
set, any subsequent operations will operate on the program memory. On Reset,
EEPROM is selected by default.
Control bits RD and WR initiate read and write, respectively. These bits cannot be
cleared, only set, in software. They are cleared in hardware at completion of the read
or write operation. The inability to clear the WR bit in software prevents the accidental,
premature termination of a write operation.
The WREN bit, when set, will allow a write operation to occur. On power-up, the WREN
bit is clear.
3.13.5.2 PIC18
3.13.5.2.1 TBLPTR
The Table Pointer (TBLPTR) points to a byte address in program space. Executing
TBLRD places the byte pointed to into TABLAT. In addition, TBLPTR can be modified
automatically for the next table read operation.
The TBLPTR is comprised of three SFR registers: Table Pointer Upper Byte, Table
Pointer High Byte and Table Pointer Low Byte (TBLPTRU:TBLPTRH:TBLPTRL).
These three registers join to form a 22-bit wide pointer.
3.13.5.2.2 TABLAT
The Table Latch (TABLAT) is an 8-bit register mapped into the SFR space. The Table
Latch register is used to hold 8-bit data during data transfers between program memory
and data RAM.
TABLE 3-39: NEW REGISTERS FOR ENHANCED MID-RANGE
Register Purpose
EEADRx Address to read/write in program or EEPROM memory
EEDATx 2-byte word that holds 14-bit data for read/write
EECON1 Control register for memory access
TABLE 3-40: NEW REGISTERS FOR PIC18
Register Purpose
TBLPTR Points to a byte address in program space
TABLAT Holds 8-bit data from program space
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